Where in the UK are you (if you are still there)? Looking at the manufacturers, it appears there are plenty of audiologists in the UK.
I haven't tried using the UV light in my hearing aid dryer, but since it is included, I would imagine it is safe since hearing aids are acrylic. The only issue I can think of is possible discoloration or premature aging of the sound tubes, but the exposure is relatively short. You can ask UE, but chances are they will say not to do it if they aren't sure.